The invention relates to a device for securing a plug with a motor involving a piston propelled by gas, particularly combustion gases. It is aimed in particular at a means improving the combustion inside the chamber in which the gases are produced.
A device of this type comprises a casing which has the overall form of a gun. This casing contains a small internal combustion engine which drives a plug guide in a translation movement. The plug guide is secured to a piston propelled by a compressed gas which is the product of the combustion of a combustible gas in the adjoining combustion chamber. The gaseous mixture comprising the air and the combustible gas is created in the chamber then ignited by an appropriate ignition means. The gun comprises a combustible-gas cartridge housed, for example, in the hand grip. When a plug is fired, a metered amount of combustible gas is sent into the chamber, then voltage is applied to the firing means. In devices known to the applicant company, the gas follows a path along the device from a metering valve near the gas cartridge to the combustion chamber. The gas is guided along a duct, generally a fine tube, arranged between the valve and the chamber.
With the devices found on the market, it is observed that there is a significant delay between the time of firing and the actual ejection of the plug. This delay may prove troublesome when the operator is in an uncomfortable position and the device is likely to move.
An object of the invention is to reduce the reaction time as far as possible.
According to the invention, this result is achieved by incorporating a means that creates a pressure drop between the part of the tube upstream of its end near the combustion chamber and the chamber itself, so as to at least partially avoid the vaporizing of the gas upstream of the said end.
Such a means consists of a narrowing of the tube at its end, the tube has a side orifice.
What happens is that the gas is normally in the liquid state in the cartridge, and experiences expansion as it leaves the metering valve. It has been observed that, surprisingly, if the time of its vaporization prior to entering the chamber is delayed, the time that the device takes to react the squeezing of the trigger is reduced.
This result can be explained by the fact that there is a link between the vaporizing of the gas as it passes through the metered valve, and the time taken to fill the combustion chamber. With devices of the prior art, the time is relatively long. By contrast, with the solution of the invention, the gas is propelled in greater quantity and in a shorter time because it remains partially in the liquid state immediately upstream of the atomization orifice. The cycle time is thus reduced.
According to another characteristic, the cross section of the orifice or of the orifices is at least 10% less than the cross section of the duct.